Fig. 1

A scheme of the complement system. Complement can be activated via three different routes. The classical and lectin pathways have their own specific pattern recognition molecules (PRMs), whereas the alternative pathway is activated by a spontaneous tick-over of C3 and deposition of C3b molecules onto permissive surfaces, which is facilitated by properdin (P). All pathways converge at the stage of C3 convertases, which catalyse breakdown of C3 into C3a and C3b molecules. When C3b molecules bind to the convertase complex, it gives rise to the C5 convertase. Except for the triggers indicated for each pathway in the scheme, apoptotic and necrotic cellular debris as well as degradative protein fragments from the extracellular matrix can also trigger all three pathways [4, 32]. In red and boldface type are the markers of complement activation analysed in our study: C4d, the end degradation product of C4b; C3bBbP, a soluble form of alternative C3 convertase including properdin; and sTCC, soluble terminal complement complex (a soluble form of C5b-9). Factor D Serine protease that cleaves factor B, Igs Immunoglobulins, MASP Mannose-binding lectin-associated serine protease, MBL Mannose-binding lectin